Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

Contactor not pulling in

I've been working on a Carrier RTU Model 50hjq014. First time found the contactor not pulling even though had correct voltage at contactor. Just touched contactor and it pulls in. I replaced contactor and it worked fine for about a month. Called back out same problem. Checked for loose wiring, bad ground (contactor 120v coil), pressure switches. Couldn't find anything wrong, but went ahead and tried another contactor. Works for about a month then same problem happens. Tried even replacing current sensing switches. And it happened again. Any suggestions would be appreciated, maybe Im missing some kind of stat or switch that is on the unit.

120 volt coil ?

Originally Posted by moseamo

I've been working on a Carrier RTU Model 50hjq014. First time found the contactor not pulling even though had correct voltage at contactor. Just touched contactor and it pulls in. I replaced contactor and it worked fine for about a month. Called back out same problem. Checked for loose wiring, bad ground (contactor 120v coil), pressure switches. Couldn't find anything wrong, but went ahead and tried another contactor. Works for about a month then same problem happens. Tried even replacing current sensing switches. And it happened again. Any suggestions would be appreciated, maybe Im missing some kind of stat or switch that is on the unit.

? are you sure that the coil is supposed to be 120 volt?

"Christ is the Son of God Who died for the redemption of sinners and was resurrected after three days. This is the greatest truth in the universe. I die because of my belief in Christ." Watchman Nee

I've seen something similar with units that have a delay on make timer on them to prevent short cycling when the stat is being fiddled with..
The timer works properly most of the time, but every so often it passes correct voltage but not enough current to pull in the coil on the contactor. When this happens you see correct voltage and the contactor still does nothing.

Does the replaced contactor work properly when 120 is applied to the coil after replacement? If so it would indicate the problem is not the contactor but the board or the stat.

IS YOUR CONTACTER CHATTERING? CHECK THE VA RATING ON YOUR TRANSFORMER SEE WHAT YOUR PULLING. IF YOUR USING WHAT EVER CONTACTOR YOU HAVE ON YOUR TRUCK IF YOU GO TO BIG YOUR TRANSFORMER MIGHT NOT BE ABLE TO PULL IT IN. TRY BUMPING UP THE SIZE OF YOUR TRANSFORMER.

I've seen something similar with units that have a delay on make timer on them to prevent short cycling when the stat is being fiddled with..
The timer works properly most of the time, but every so often it passes correct voltage but not enough current to pull in the coil on the contactor. When this happens you see correct voltage and the contactor still does nothing.

Does the replaced contactor work properly when 120 is applied to the coil after replacement? If so it would indicate the problem is not the contactor but the board or the stat.

Yes new contactor works fine for about a month. Next time it happens Ill try checking how much current the coil is pulling. Never thought of that.

IS YOUR CONTACTER CHATTERING? CHECK THE VA RATING ON YOUR TRANSFORMER SEE WHAT YOUR PULLING. IF YOUR USING WHAT EVER CONTACTOR YOU HAVE ON YOUR TRUCK IF YOU GO TO BIG YOUR TRANSFORMER MIGHT NOT BE ABLE TO PULL IT IN. TRY BUMPING UP THE SIZE OF YOUR TRANSFORMER.

referjman, turn off the capslock, it's like you're yelling !

Check the inrush and holding VA requiremenrs for the contactor, had 1 recently that worked fine when I was there but 4 hours later it wouldn't pull in. The holding current was 22VA but the inrush was 75VA. Transformer was, you guessed it 75VA. That was on 24VAC circuit but I have also seen it happen on 120 control circuits. If you can find out what Original Make/Model was, that may solve your problem. Also check to see if you have a pilot relay that controls the contactor, that deserves a look also.

If sense were so common everyone would have it !

Any advice provided is worth exactly what you paid for it, not a penny more not, a penny less !!